Silicon/organic Semiconductor Composite Optoelectronic Materials And Devices

Silicon is the basic material of modem electronic industry,but the low luminescence efficiency due to its indirect band gap excludes its further application in optoelectronic integration,which is important for future information technology. Organic semiconductor is cheap,easily processible and can luminesce efficiently. Fabricating organic-emitting diodes based on silicon is believed to be a possible route to achieve silicon-based optoelectronic integration.At the same time,some novel phenomena and structures can be found via the study on the energy transfer and charge transfer which may exist in the silicon/organic semiconductor composite systems.So the study on silicon/organic semiconductor composites and devices is not only significant in theory but also can impel the application of silicon/organic semiconductor composites and devices.PS was prepared by electrochemical anodization of p-type Si wafers.The influences of time on the morphology,photoluminescence(PL) spectra and surface photovoltaic spectra(SPS) of PS were investigated.The results showed that the longer etching time corresponded to the greater porosity of PS,which was explained via the formation mechanism of PS.Then the quantum confinement - luminescence center (QC-LC) model was employed to interpret the PL of PS.The model told that the photoexcited electron-hole pairs mainly occurred in the nano-Si-particles(NSPs) in PS,which could be used to explain the blue-shift of absorption peaks showed in SPS of PS.A n-type semiconductor-N,N'-diphenyl-3,4,9,10-perylenetetracarboxylic diimide(DPP) was synthesized and its energy band structure was investigated via UV-vis absorption spectra and cyclic voltammogram(CV) measurements.DPP was then embedded into PS by electrodeposition to form DPP/PS composites.Scanning electron microscope(SEM),PL spectra and SPS were employed to investigate the properties of the composites.According to the SEM images,the larger aperture helped the electrodeposition of DPP molecules into PS,leading to a larger interfacial area between DPP and PS.The PL quenching and stronger surface photovoltaic response resulting from the formation of the heterojunctions revealed a charge transfer process taking place in the composites.This process was even more intense in the composites based on PS with a longer etching time due to their larger interfacial area.The exciton dissociation efficiency was improved in the DPP/PS composites compared to that of PS,and could also be adjusted by the PS etching time,which we think was very important to fabricate solar cells based on PS.Silicon NPs were synthesized by using a solution-phase method.Silicon NPs could luminesce due to the quantum confinement effect.Poly(9-vinyl carbazole) (PVK),a hole transport polymer,was employed to composite with silicon NPs,and the PVK/silicon NPs composites with different silicon NPs content were fabricated by solution-blending method.The excellent overlap between the PL of PVK and the absorption of silicon NPs could also be observed from the PL spectra of PVK and the UV-vis absorption spectra of silicon NPs,which was the fundament of FRET from PVK to silicon NPs.A F(?)rster critical distance of about 51(?) was calculated from the overlap of the spectra.PL spectra of the composite films showed the enhancement of the PL intensity of silicon NPs in the composite films when both PVK and the silicon NPs were excited.PLE spectra revealed that the PL of silicon NPs in the composite films originated from photoexcitations in both PVK and silicon NPs.The PL and PLE results showed that FRET took place from PVK to silicon NPs in their composite films.The results of time-resolved PL decays showed the PL lifetime of silicon NPs was prolonged from 1.11 ns to 1.44,1.65,and 1.91 ns with increasing the content of silicon NPs from 0%to 0.2%,0.4%and 0.8%in the composite films,while that of PVK was decreased from 7.24 ns to 5.24,5.90,and 4.19 ns correspondingly.This was what expected in the presence of FRET.The decay kinetics yielded R0= 47A which was close to the one(51 A) calculated from the overlap of the spectra.At last,the energy transfer efficiency with a maximal value of 0.42 and the energy transfer rate with a maximal value of 11.10×10⁷s^-1 were also calculated from the decay kinetics. The results indicated that the prepared composites had potential application in polymer/inorganic NPs hybrid light-emitting diodes.N-dodecyl-N'-phenyl-3,4,9,10-perylenetetracarboxylic diimide(DOPP) was synthesized and characterized.DOPP/silicon NPs composites with different silicon NPs content were fabricated by solution-blending method.Remarkable photoluminescence(PL) quenching was observed in the composites dispersed in polymethyl methacrylate matrix.Considering the large overlap of the PL of silicon NPs and the absorption of DOPP,FRET from silicon NPs to DOPP might take place. For a composite with 10%DOPP,FRET only accounted for 22.4%of the total photogenerated excitons.On the other hand,a 78%decrease of the PL intensity of silicon NPs in the composite was observed.The low energy transfer efficiency and large PL intensity decrease strongly suggest a different mechanism which results in the PL quenching of silicon NPs in the composites.The energy band structure of DOPP and silicon NPs were investigated via CV measurement.The results showed that an electron energy transfer occurred from silicon NPs to DOPP.The results of time-resolved PL spectra showed that the lifetime of silicon NPs was prolonged in the silicon NPs/DOPP composites compared to that of the pure silicon NPs,which revealed that the electron transfer predominated the PL quenching.The photoconductivity of the composites was studied,and the photosensitivity enhancement of the composites was realized due to the photoinduced electron transfer between silicon NPs and DOPP.P-type silicon wafers were used as anodes to fabricate organic light-emitting diodes(OLEDs).The hole injection for the device with a silicon anode was superior to the device with an ITO anode,which also gave a greater carrier injection imbalance. 5-F-tris-(8-hydroxy-quinolinato) aluminum(5FAlq₃) was employed as electron transporting material to fabricate OLEDs with silicon anodes,and the results showed that it could ameliorate the cartier injection imbalance.But the performance of the device was not improved because the electron transporting layers and luminous layers were not separated completely.The complete separation of the electron transporting and luminous layers could be achieved via the using of the hole blocking material (BCP).Thus the performance of the devices was improved greatly.The highest power efficiency was improved from 0.117 to 0.462 lm/W,On the other hand,the resistivity of silicon anodes had a great influence on the performance of the devices.It was shown that the device with an 1Ωcm silicon anode had the best performance,which indicated that the best carrier injection balance was achieved in this device.